A broadband wireless access system according to a related art will be explained in general as follows. Unlike the conventional 2G or 3G mobile communication systems, an IEEE 802.16e system, for which international standardization of a broadband wireless access system is in progress, is not provided with a hierarchical structure for a home location register (HLR), a visitor location register (VLR), a mobile switching center (MSC), a base station controller (BSC), a radio network controller (RNC) and the like. However, the IEEE 802.16e system includes a mobile subscriber station (MSS) as a mobile terminal, a base station (BS) and an authentication service authorization (ASA) as an authentication managing server. Furthermore a common physical layer (PHY) and a medium access control (MAC) layer are defined between the base station and the mobile subscriber station.
FIG. 1 is a diagram of a frame structure for an orthogonal frequency division multiple access (OFDMA) physical layer in a broadband wireless access system. Referring to FIG. 1, a downlink subframe starts with a preamble used for synchronization and equalization in a physical layer. Following, the preamble is a broadcast-formatted downlink map (DL-MAP) message defining positions and usages of bursts allocated to a downlink and uplink and a frame control header (FCH). An uplink map (UL-MAP) message follows the DL-MAP and FCH to define a structure of an entire frame.
Examples of DL-MAP and UL-MAP messages are shown in Table 1 and Table 2, respectively.
TABLE 1SyntaxSizeNotesDL-MAP_Message_Format( ) { Management Message Type = 28 bits PHY Synchronization FieldvariableSee appropriate PHYspecification. DCD Count8 bits Base Station ID48 bits  Begin PHY Specific Section {See applicable PHYsection.  for(i=1; i <= n;i++) {For each DL-MAPelement 1 to n.   DL-MAP-IE( )variableSee corresponding PHYspecification.   } }if !(byte boundary) {Padding Nibble4 bitsPadding to reach byteboundary. }}
TABLE 2SyntaxSizeNotesUL-MAP_Message_Format( ) { Management Message Type = 38 bits Uplink Channel ID8 bits UCD Count8 bits Allocation Start Time32 bits  Begin PHY Specific Section {See applicable PHYsection.  for(i=1; i <= n;i++) {For each UL-MAPelement 1 to n.   UL-MAP-IE( )variableSee corresponding PHYspecification.   }  } if !(byte boundary) { Padding Nibble4 bitsPadding to reach byteboundary.  } }
In a burst mode physical layer, a DL-MAP message defines usages of bursts allocated to a downlink interval and a UL-MAP message defines usages of bursts allocated to an uplink interval. For information elements configuring the DL-MAP message, as shown in Table 3, a downlink traffic interval is identified at a user end by a downlink interval usage code (DIUC), a connection identifier (CID) and burst position information (e.g. subchannel offset, symbol offset, subchannel no., and symbol no.). For information elements configuring the UL-MAP message, as shown in Table 4, usage is determined by an uplink interval usage code (UIUC) per connection identifier (CID). A position of a corresponding interval is regulated by duration. In this case, a usage per interval is determined according a UIUC value used in the UL-MAP. Each interval starts at a point having some distance from a previous information element (IE) start point regulated by the UL-MAP IE.
TABLE 3SyntaxSizeNotesDL-MAP_IE( ) { DIUC4 bits if (DIUC == 15) { Extended DIUCvariabledependent IE } else {  if (INC_CID == 1)The DL-MAP starts withINC_CID = 0. INC_CID is toggled{between 0 and 1 by theCID-SWITCH_IE( ). N_CID8 bitsNumber of CIDs assigned for this IE  for (n=0; n<_CID;n++) {   CID16 bits   } } OFDMA symbol8 bitsoffset Subchannel offset6 bits Boosting3 bits000: normal (not boosted); 001: +6 dB;010: −6 dB; 011: +9 dB; 100: +3 dB;101: −3 dB; 110: −9 dB; 111: −12 dB No. OFDMA7 bitsSymbols No. Subchannels6 bits Reception Coding2 bits0b00 - No repetition coding 0b01 -IndicationRepetition coding of 2 used 0b10 -Repetition coding of 4 used 0b11 -  }Repetition coding of 6 used}
TABLE 4SyntaxSizeNotesUL-MAP_IE( ) { CID16 bits  UIUC4 bits If (UIUC == 12) { OFDMA symbol offset8 bits Subchannel offset7 bits No. OFDMA Symbols7 bits No. Subchannels7 bits Ranging Method2 bits0b00 - Initial ranging over twosymbols 0b01 - Initial Rangingover four symbols 0b10 - BWRequest/Periodic Ranging overone symbol 0b11 - BWRequest/Periodic Rangingover three symbols reserved1 bitShall be set to zero} else if (UIUC == 14) { CDMA_Allocation_IE( )32 bits   else if (UIUC == 15){ Extended UIUCvariabledependent IE } else { Duration10 bitsIn OFDMA slots Reception Coding2 bits0b00 - No repetition codingIndication0b01 - Repetition coding of 2used 0b10 - Repetition coding of4 used 0b11 - Repetition codingof 6 used  } Padding nibble, if needed4 bitsCompleting to nearest byte,shall be set to 0.}
The frame control header (FCH) preceding the DL-MAP is a header that indicates coding information and a length of the DL-MAP. Table 5 shows a frame structure of the FCH.
TABLE 5SyntaxSizeNotesDL_Frame_Prefix_Format( ) {Used subchannel bitmap6 bitsBit #0: Subchannels 0-11 are usedBit #1: Subchannels 12-19 are usedBit #2: Subchannels 20-31 are usedBit #3: Subchannels 32-39 are usedBit #4: Subchannels 40-51 are usedBit #5: Subchannels 52-59 are usedRanging_Change_Indication1 bit Repetition_Coding_Indication2 bit 00 - No repetition coding on DL-MAP01 - Repetition coding of 2 used on DL-MAP10 - Repetition coding of 4 used on DL-MAP11 - Repetition coding of 6 used on DL-MAPCoding- Indication3 bits0b000 - CC encoding used on DL-MAP0b001 - BCC encoding used on DL-MAP0b010 - CTC encoding used on DL-MAP0b011 - ZT CC used on DL-MAP0b100 to 0b111 - ReservedDL_MAP_Length8 bitsreserved4 bitsShall be set to zero}
Table 6 shows an example of a neighbor advertisement (MOB_NBR-ADV) message as a broadcast message of a neighbor base station. A base station periodically broadcasts information about neighbor base stations via the MOB_NBR-ADV message. A mobile subscriber station receives the message and refers to it for scanning and handover.
TABLE 6SyntaxSizeNotesMOB_NBR-ADV_Message_Format( ) {Management Message8 bitsType = 53Skip-Optional-Fields8 bitsBit [0]: if set to 1, omit Operator ID bitmapfieldBit [1]: if set to 1, omit NBR BS ID fieldBit [2]: if set to 1, omit HO process optimization fieldBit [3]: if set to 1, omit QoS related fieldsBits [4] to [7]: reservedIf (Skip-Optional-Fields-[0]=0) {Operator ID24 bits Unique ID assigned to the operator}Configuration  Change8 bitsIncremented each time the Countinformation for the associated neighbor BS has changed.Fragmentation Index4 bitsThis field indicates the current fragmentation index.Total Fragmentation4 bitsThis field indicates the total number of fragmentations.N_NEIGHBORS8 bitsFor (j=0 ;j<N_NEIGHBORS ; j++){Length8 bitsLength of message information within the iteration of N_NEIGHBOR in bytes.PHY Profile ID8 bitsAggregated IDs of Co-located FA Indicator, FA ConfigurationIndicator, FFT size, Band-width, Operation Mode of the startingsub-channelization of a frame and Channel Numberif (FA Index Indicator==1) {FA Index8 bitsThis field, Frequency Assignment Index, is present only the FA Index Indicator in PHY Profile ID is set.Otherwise, the neighbor BS has the same FA Index or the centerfrequency is indicated using the TLV encoded information.}if (BS EIRP Indicator ==1) {BS EIRP8 bitsSigned Integer from −128 to 127 in unit of dBm. This field is present only if the BS EIRP indicator is set in PHY Profile ID.Otherwise, the BS has the same EIRP as the serving BS.}if (Skip-Optional-Fields[1]=0) {Neighbor BSID24 bits This is an optional field for OFDMA PHY and it is omitted orskipped if Skip Optional Fields Flag = 1.}Preamble8 bitsThe index for the PHY profile Index/Subchannel Indexspecific preamble. Preamble Index is PHY specific for SCa and OFDMA. The value of PreambleIndex shall be ignored and a value of 0x00 shall be used for OFDM PHY. For the SCa and OFDMA PHY this parameter defines the PHY specific preamble. For the OFDM PHY the 5 LSB contain the active DL subchannel index. The 3 MSB shall be reserved and set to 0b000.if (Skip-Optional-Fields[2]=0) {HO Process Optimization8 bitsHO Process Optimization is provided as part of this message isindicative only. HO process requirements may change at time ofactual HO.For each Bit location, a value of 0 indicates the associated reentrymanagement messages shall be required, a value of 1 indicates thereentry management message may be omitted.Regardless of the HO Process Optimization TLV settings, thetarget BS may send unsolicited SBC-RSP and/or REG-RSPmanagement messages.Bit #0: Omit SBC-REQ/RSP management messages during current reentry processingBit #1: Omit PKM-REQ/RSP management messages duringcurrent reentry processingBit #2: Omit REG-REQ/RSP management messages duringcurrent reentry processingBit #3: Omit Network Address Acquisition management messagesduring current reentry processingBit #4: Omit Time of Day Acquisition management messagesduring current reentry processingBit #5: Omit TFTP management messages during current reentryprocessingBit #6: Full service and operational state transfer or sharing between serving BS and target BS (ARQ, timers, counters, MAC state machines, etc.Bit #7: Reserved}if (Skip-Optional-Fields-[3]=0) {Scheduling Service4 bitsBitmap to indicate if BS supports a Supportedparticular scheduling service, 1 indicates support, 0 supports not supportbit 0: Unsolicited Grant Service (UGS)bit 1: Real-time Polling Service (rtPS)bit 2: Non-real-time Polling service (nrtPS)bit 3: Best Effort value of ?000? indicates no information on service availableAvailable Radio Resource4 bitsPercentage of reported average available subchannels and symbolsresources per frame0000: 0%0001: 20%0010: 40%0011: 60%0100: 80%0101: 100%0110-1110: reserved0110-1110: reserved value of 1111 indicates no information on service availableReserved8 bitsShall be set to zero}DCD Configuration4 bitsThis represents the 4 LS bits of the Change CountNeighbor BS current DCD configuration change countUCD Configuration4 bitsThis represents the 4 LS bits of the Change CountNeighbor BS current UCD configuration change countTLV Encoded NeighborvariableTLV specificinformation}}
Table 7 and Table 8 are embodiments of a basic capability request (SBC-REQ) message and a basic capability response (SBC-RSP) message, respectively. The mobile subscriber station having received the DL-MAP and UL-MAP executes ranging for a network access procedure and transmits an SBC-REQ message to the base station to initiate a negotiation for basic capability. In response to the negotiation, the base station sends an SBC-RSP message about a portion coinciding with its performance.
TABLE 7SyntaxSizeNotesSBC-REQ_Message_Format( ) {Management Message Type = 268 bitsTLV Encoded InformationvariableTLV specific}
TABLE 8SyntaxSizeNotesSBC-RSP_Message_Format( ) {Management Message Type = 278 bitsTLV Encoded AttributesvariableTLV specific}
Once the negotiation for basic capability is completed, the mobile subscriber station executes a registration procedure via a registration request (MOB-REG-REQ) message and a registration response (MOB-REG-RSP) message. Table 9 and Table 10 show examples of the MOB-REG-REQ and MOB-REG-RSP messages, respectively.
TABLE 9SyntaxSizeNotesREG-REQ_Message_Format( ) {Management Message Type = 48 bitsDownlink Channel ID8 bitsTLV Encoded InformationvariableTLV specific}
TABLE 10SyntaxSizeNotesREG-RSP_Message_Format( ) {Management Message Type = 58 bitsUplink Channel ID8 bitsTLV Encoded InformationvariableTLV specific}
Media independent handover (MIH) technology will now explained. An object of an IEEE 802.21 system, in progress for the international standardization of inter-heterogeneous-network media independent handover, is to enhance user convenience for mobile terminal devices by providing seamless handover and service continuity between heterogeneous networks. An MIH function, event trigger, command service and information service (IS) are defined as basic requirements of the IEEE 802.21 system.
A mobile subscriber station is a multi-node that supports at least one interface type, wherein an interface can be implemented in various types. Possible interface types include a wire-line type interface such as an IEEE 802.3-based Ethernet, wireless interface types based on IEEE 802.XX including IEEE 802.11, IEEE 802.15, IEEE 802.16 or the like, and interfaces defined by a cellular standardization organization such as 3GPP and 3GPP2, for example.
FIG. 2 is an exemplary diagram of a multi-mode mobile subscriber station. Referring to FIG. 2, a multi-mode mobile subscriber station includes a physical layer (PHY) per mode and a medium access control (MAC) layer per mode. Furthermore, an MIH layer lies below an IP layer.
Media independent handover (MIH) is defined between IEEE 802-series interfaces or between an IEEE 802-series interface and a non-IEEE 802-series interface, such as a 3GPP or 3GPP2 interface. Also, a mobility supporting protocol of an upper layer such as a Mobile IP and session initiation protocol (SIP) is supported for the seamless handover service.
A network registration procedure in initializing a broadband wireless access system is explained as follows. FIG. 3 is a flowchart of a mobile station initializing procedure in a broadband wireless access system. Referring to FIG. 3, once power of a mobile subscriber station is turned on, the mobile subscriber station searches a downlink channel and acquires uplink/downlink synchronization with a base station via a DL-MAP and a UL-MAP (1). The mobile subscriber station adjusts uplink transmission parameters by ranging with the base station via RNG-REQ and RNG-RSP messages, and the base station allocates a basic management connection identifier (CID) and a primary management CID to the mobile subscriber station (2). The mobile subscriber station then negotiates for a basic capability with the base station via SBC-REQ and SBC-RSP messages (3). Afterward, authorization is carried out on the mobile subscriber station (4). The mobile subscriber station then performs a registration procedure to the base station via REG-REQ and REG-RSP messages, wherein the base station allocates a secondary management CID to the mobile subscriber station managed by an Internet protocol (IP) (5). Once an IP connection is created (6), a current date and time are set (7). A configuration file of the mobile subscriber station is then downloaded from a trivial file transfer protocol (TFTP) server (8), and a connection for a prepared service is created (9).
In media independent handover (MIH), an MIH function is placed below an IP layer and facilitates a handover handling process using a trigger event and an input value from a second layer (Layer 2), such as information of other networks and the like. The MIH function can include input values based on user policy and configuration that may influence a handover process. General interfaces are defined between the MIH function and a third layer (Layer 3) entity such as a mobile Internet protocol (Mobile IP) and a session initiation protocol (SIP). These interfaces provide information about a first layer (physical layer), the second layer (Layer 2) (MAC layer) and mobility management. The MIH acquires information about lower layers and a network with the help of the event and information service. Accordingly, the MIH function should be placed in a higher layer to monitor and control statuses of other links within the mobile subscriber station. FIG. 4 is a diagram of functional entities and a transport protocol of a terminal including an MIH function and a network, in which dotted lines indicate a primitive, an event trigger and the like.
An event trigger for handover between heterogeneous networks is explained as follows. For fast handover, a network layer needs to use information from a link layer to re-establish a connection as soon as possible. A link layer event helps to estimate a user's movement and may help a mobile subscriber station and network prepare handover in advance. A trigger for handover may begin with a physical layer (PHY) and a medium access control layer (MAC). An origin of this trigger may be a local stack or a remote stack. FIG. 5 is a diagram of a trigger model.
An event trigger provides a state of a current signal, a state change of another network and an estimated change. The event trigger also provides information regarding a change between a physical layer and a medium access control layer and attribute changes of a specific network. Event types can be classified into the following: (1) PHY layer event; (2) MAC layer event; (3) Management event; (4) L3 event; and (5) Application event.
Basic trigger events will now be explained. A “Link_Up” trigger event occurs when a Layer 2 (L2) connection is established on a specific link interface and when Layer 3 (L3) packets can be transferred from a higher layer. In this case, it is decided that all L2 configurations configuring the link are completed. Event origins are a Local MAC and a Remote MAC. Parameters are shown in Table 11.
TABLE 11NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin from which event is generatedEventDestinationEVENT_LAYER_TYPEDestination to which event shall be deliveredMacMobileTerminalMAC AddressMAC address of MSSMacOldAccessRouterMAC AddressMAC address of old access routerMacNewAccessRouterMAC AddressMAC address of new access routerNetworkIdentifierMedia SpecificNetwork Identifier usable in detecting change ofsubnetIP_Renewal_IndicatorIndicating necessity of changing temporary IPaddress.0: change unnecessary1: change necessary
A “Link Down” trigger event occurs when an L2 connection is released on a specific interface and when it is no longer able to transfer L3 packets. An event origin is a Local MAC. Parameters are shown in Table 12.
TABLE 12NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin from which event is generatedEventDestinationEVENT_LAYER_TYPEDestination to which event shall be deliveredMacMobileTerminalMAC AddressMAC address of MSSMacOldAccessRouterMAC AddressMAC address of old access routerReasonCodeReason why link is released
A “Link Going Down” trigger event occurs when it is estimated that an L2 connection is going to link down within a specific time. The “Link Going Down” trigger event may be a signal for initializing a handover procedure. Event origins are a Local MAC and a Remote MAC. Parameters are shown in Table 13.
TABLE 13NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin from which event is generatedEventDestinationEVENT_LAYER_TYPEDestination to which event shall be deliveredMacMobileTerminalMAC AddressMAC address of MSSMacOldAccessRouterMAC AddressMAC address of old access routerMacNewAccessRouterMAC AddressMAC address of new access routerTimeIntervalTime in msecsEstimated time for Link_UpConfidenceLevel%Estimated level for Link_Down of link in a specifictimeUniqueEventIdentifierUsed in case that Event rollback occurs
A “Link Going Up” trigger event occurs when it is estimated that an L2 connection is going to link up within a specific time. The “Link Going Up” trigger event is used in case when a long duration of time is required for a network to be initialized. Event origins are a Local MAC and a Remote MAC. Parameters are shown in Table 14.
TABLE 14NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin from which event is generatedEventDestinationEVENT_LAYER_TYPEDestination to which event shall be deliveredMacMobileTerminalMAC AddressMAC address of MSSMacOldAccessRouterMAC AddressMAC address of old access routerMacNewAccessRouterMAC AddressMAC address of new access routerTimeIntervalTime in msecsEstimated time for Link_UpConfidenceLevel%Estimated level for Link_Up of link in a specific timeUniqueEventIdentifierUsed in case that Event rollback occurs
A “Link_Available” trigger event indicates that a new specific link is usable or available. Furthermore, the “Link_Available” event indicates the possibility that a new base station or access point (AP) or point of attachment (POA) can provide a link having a better quality than that of a base station or AP or POA currently accessed by a mobile subscriber station. Event origins are a Local MAC and a Remote MAC. Parameters are shown in Table 15.
TABLE 15NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin from which event is generatedEventDestinationEVENT_LAYER_TYPEDestination to which event shall be deliveredMacMobileTerminalMAC AddressMAC address of MSSMacOldAccessRouterMAC AddressMAC address of old access routerMacNewAccessRouterMAC AddressMAC address of new access routerIP_Renewal_IndicatorIndicating necessity of changing temporary IPaddress.0: change unnecessary1: change necessary
An information service for inter-heterogeneous-network handover will now be explained. A media independent information service (MIIS) provides a similar frame network on a hierarchical heterogeneous network to facilitate a search and selection of various kinds of present networks. Namely, the media independent information service (MIIS) provides detailed information about a network needed to search and select a network and should be accessible from any kind of networks. The media independent information service (MIIS) should include the following information elements such as link access parameter, security mechanism, neighbor map, location, provider and other access information, cost of link and the like.
FIG. 6 is a flowchart of a procedure for acquiring an information service according to a related art. Referring to FIG. 6, an MIH of a mobile subscriber station (MS) transfers an MIH_info.request message to its MAC to request an information service (S610). The MAC of the mobile subscriber station then transfers an information request frame to a base station (BS) (S620). A MAC of the base station delivers the information request from the mobile subscriber station to its MIH via MIH_Info.indication message (S630). The MIH of the base station then delivers a retained media independent information service to the MAC layer via a MIH_Info.response message (S640). This enables the MAC of the base station to send an information response frame in response to the mobile subscriber station (S650). The MAC of the mobile subscriber station receives the information response frame and delivers contents of the received information service to its MIH via an MIH_Info.confirm message (S660).
However, in the related art for the broadband wireless access system, a multi-mode mobile subscriber station attempting handover to a broadband wireless access system from another interface network (e.g., IEEE 802.11, 3GPP or 3GPP2), a mobile subscriber station attempting handover to another base station in the same broadband wireless access system, or a mobile subscriber station executing an initial network access procedure within a base station of a broadband wireless access system, is unable to know whether an MIH capability of a base station is available. Accordingly, what is needed is an invention that resolves the problems of the related art.